Pushing a graphical user interface to a remote device with display rules provided by the remote device

ABSTRACT

A graphical user interface (“GUI”) can be presented on a remote control accessory device that has user input and display devices. The GUI can be defined and managed by a portable media device that is controlled using the GUI. The portable media device can provide the accessory with a GUI image to be displayed. The accessory can send information to the portable media device indicative of a user operation of an input device in response to the displayed image. The portable media device can process this input to identify the action requested by the user and take the appropriate action, which can include updating the GUI image provided to the accessory.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. application Ser. No. 12/683,218 filed Jan. 6, 2010, entitled “Pushing a User Interface to a Remote Device,” which is a continuation-in-part of U.S. application Ser. No. 12/119,960 filed May 13, 2008, entitled “Pushing a User Interface to a Remote Device.” The respective disclosures of both applications are incorporated by reference herein in their entirety.

BACKGROUND

The present disclosure relates generally to accessories for portable media devices and in particular to allowing a portable media device to provide a user interface for controlling the media device to an accessory.

Portable media devices allow users to store media content (music, videos, photos, audiobooks, etc.) and access stored media content from nearly anywhere. Some portable media devices also allow users to connect other devices (referred to herein as “accessories” or “accessory devices”) to the portable media device, thereby enhancing some aspect of the portable media device's operation. For example, most portable media devices provide a headphone jack for listening to audio content. Some accessories provide speakers, thus allowing the user to share the sound with others, or to listen in environments where use of headphones might not be feasible (such as while driving).

In some instances, an accessory can be used to control operation of a portable media device; such accessories are referred to herein as “remote control devices.” The remote control device can send commands to the portable media device indicating a user-requested operation (such as starting or pausing playback, skipping to the next track, returning to a previous track, fast-forward or rewind within a track, etc.). The portable media device can execute the requested operation, thus allowing the user to operate the portable media device without touching the portable media device. Such remote control operation can be particularly useful in situations where it is inconvenient for a user to manipulate the portable media device's interface directly. For example, portable media devices tend to be small, with relatively small controls and display screens. Thus, it can be difficult for a user to operate such a device while driving or from across a room.

Some remote control devices provide a graphical user interface (GUI) and allow the user to perform more advanced functions such as browsing a database of stored content, selecting content to play, etc. For instance, Johnson Controls International has been developing a “Mobile Device Gateway” for use in vehicles; the system includes a connection point for a portable media device and a console that provides an audio/visual interface. But existing remote GUIs are defined and controlled by the remote control device, and consequently, they may bear little resemblance to a GUI supplied by the portable media device itself. Certain functions available on the portable media device (such as browsing or searching a database, adjusting playback settings, etc.) may be unavailable or difficult to find. Thus, a user may not be able to perform desired functions. Further, GUIs provided for the same portable media device by different remote control devices might be quite different, and the user who connects a portable media device to different accessories with remote control may find the inconsistencies frustrating.

It would, therefore, be desirable to provide a more consistent remote user interface experience.

SUMMARY

Embodiments of the present invention relate to providing a graphical user interface (“GUI”) on a remote control accessory device, where the GUI can be defined and managed by a portable media device rather than the accessory device. The accessory device can provide a combination of user input and visual feedback devices, such as a video screen for presenting information and feedback to a user, along with buttons, knobs, touchscreen and/or touchpad for receiving user input. The portable media device can provide the accessory with an image (referred to herein as a “remote” GUI image) to be displayed on the video screen; the image can include various user interface elements that can resemble or replicate a “native” GUI provided directly on the portable media device. The accessory can send information to the portable media device indicative of a user action taken in response to the displayed image; such information can indicate, for example, that a particular button was pressed or that a particular portion of a touch-sensitive display screen was touched by the user. The portable media device can process this input to identify the action requested by the user and take the appropriate action. The action may include providing to the accessory an updated GUI image to be displayed, where the updated GUI image reflects the user action.

In some embodiments, a portable media device can supports a number of different functionalities (e.g., audio playback, video playback, still image playback, telephone, World

Wide Web browser, maps and navigation, etc.), and an accessory can use the remote GUI to access any or all of these functionalities. The set of functionalities accessible via the remote GUI can be determined by the portable media device or the accessory. In one embodiment, the accessory can specify which of the functionalities supported by the portable media device should be made available via the remote GUI. In another embodiment, the portable media device can make the selection. In either case, the selection can be based in part on information about the operating environment or status of the accessory.

The following detailed description together with the accompanying drawings will provide a better understanding of the nature and advantages of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates a portable media device, and FIGS. 1B and 1C illustrate accessory devices with remote graphical user interfaces for the portable media device of FIG. 1A according to embodiments of the present invention.

FIG. 2 is a block diagram of a system including a portable media device and an accessory according to an embodiment of the present invention.

FIG. 3 is a table of commands usable to implement a remote graphical user interface (“GUI”) according to an embodiment of the present invention.

FIG. 4 is a table of commands usable to implement a remote GUI according to another embodiment of the present invention.

FIG. 5 is a flow diagram of a process that can be used to provide a remote GUI for a portable media device on an accessory device according to an embodiment of the present invention.

FIG. 6 is a flow diagram of a process that can be used in an accessory to support a remote GUI according to an embodiment of the present invention.

FIG. 7 is a flow diagram of a process that can be used in a portable media device to provide a remote GUI to an accessory according to an embodiment of the present invention.

FIG. 8 illustrates a native GUI of a portable media device.

FIGS. 9A and 9B illustrate remote GUI images for an accessory according to embodiments of the present invention.

FIG. 10 is a flow diagram of a process usable to generate a remote GUI image according to an embodiment of the present invention.

FIG. 11 illustrates character size and spacing parameters that can be specified by a display rule according to an embodiment of the present invention.

FIG. 12 illustrates determination of character size based on an angular size parameter that can be specified by a display rule according to an embodiment of the present invention.

DETAILED DESCRIPTION

Embodiments of the present invention relate to providing a graphical user interface (“GUI”) on a remote control accessory device that is defined and managed by a portable media device rather than the accessory device. The accessory device provides a combination of user input and visual feedback devices, such as a video screen for presenting information and feedback to a user, along with buttons, knobs, touchscreen and/or touchpad for receiving user input. The portable media device can provide the accessory with an image to be displayed on the video screen; the image can include various user interface elements that can resemble or replicate the GUI provided directly on the portable media device. The accessory can send information to the portable media device indicative of a user action taken in response to the displayed image; such information can indicate, for example, that a particular button was pressed or that a particular portion of a touch-sensitive display screen was touched by the user. The portable media device can process this input to identify the action requested by the user and take the appropriate action. The action may include providing to the accessory an updated GUI image to be displayed, where the updated GUI image reflects the user action.

FIGS. 1A and 1B show portable media device (“PMD”) 102 and accessory 104 according to an embodiment of the present invention. In FIG. 1A, PMD 102 has a user interface that can include display screen 106 and user input device 108 (e.g., a click wheel as found on certain iPod™ media players manufactured and sold by Apple Inc., assignee of the present application). Display screen 106 can present a GUI image to the user, and the user can interact with the GUI image by operating user input device 108. Thus, for example, the user can navigate a database of stored media content, select one or more media assets to be played, control playback, and adjust settings of PMD 102. The interface provided by display screen 106 and input device 108 is referred to herein as the “native GUI” of PMD 102.

FIG. 1A shows an example of a native GUI image that can be displayed by one embodiment of PMD 102. In this example, native GUI image 101 includes an album name (“ALBUM”) at the top and a listing of tracks beneath. A currently selected track (“Track 5”) is highlighted. Up and down arrows 105, 107 indicate that scrolling to view additional tracks is possible, and a slider element 109 indicates the approximate position of the currently selected track within the list of tracks.

PMD 102 also has a connector 110 disposed on its bottom surface 112. Connector 110 provides a mechanical and electrical coupling to other devices.

Referring to FIG. 1B, accessory device (also referred to as “accessory”) 104 can be an in-vehicle media control unit that can be installed in a dashboard of a vehicle such as an automobile, on a vehicle seat back (e.g., in an automobile or airplane), or elsewhere. Accessory 104 can include display 114 and buttons 116 a-h arranged near the edges of display 114. Buttons 116 can provide “soft keys” whose function can be interpreted by accessory 104 based on what is currently displayed on display 114.

In operation, accessory 104 can play media content. For example, accessory 104 can display video content on display 114 and/or deliver the video content to another display device (e.g., on the back of a driver or passenger seat). Accessory 104 can deliver audio content to the vehicle's speaker system. Accessory 104 can also provide control for other functionality; for example, accessory 104 may provide environmental controls (heater, air conditioning); navigation-related controls (interactive maps, driving directions); controls for a radio tuner, DVD player, or the like; and so on.

Accessory 104 can also include a docking bay 118 adapted to receive PMD 102. For example, docking bay 118 can be sized and shaped to receive at least the bottom portion of PMD 102 and can include a connector 120 that mates with connector 110 of PMD 102, thereby allowing electrical signals to be transmitted back and forth between PMD 102 and accessory 104. In an alternative embodiment, PMD 102 and accessory 104 can each be equipped with a wireless communication interface (e.g., an interface implementing Bluetooth standards), thereby allowing the two devices to exchange information without a direct physical connection being made.

In accordance with an embodiment of the present invention, when PMD 102 of FIG. 1A is connected to accessory 104 of FIG. 1B, accessory 104 can enter a “remote GUI” operating mode. In this operating mode, PMD 102 can provide a GUI image to accessory 104. Accessory 104 can display the image on display 114. This remote GUI image can be displayed as received, without modification by accessory 104, thereby allowing PMD 102 to control the look of the interface. In some embodiments, PMD 102 provides a remote GUI image that replicates the native GUI of PMD 102. In other embodiments, PMD 102 can provide a remote GUI image that conforms to a modified version of the native GUI. For example, the modified GUI may use different fonts or color schemes, or may include additional or different control options. Certain aspects of the remote GUI image, such as sizes of image elements and accessible functionality can be modified based on commands from the accessory, as described below.

In FIG. 1B, display 114 of accessory 104 displays an example remote GUI image 111. Like native GUI image 101 shown in FIG. 1A, remote GUI image 111 includes an album name (“ALBUM”) at the top and a listing of tracks beneath. A currently selected track (“Track 5”) is highlighted. Up and down arrows 113, 115 indicate that scrolling to view additional tracks is possible, and a slider element 117 indicates the approximate position of the currently selected track within the list of tracks. Up arrow 113 and down arrow 115 are placed adjacent to buttons 116 e and 116 h, respectively, thereby indicating that button 116 e can be used to move up the list while button 116 h can be used to move down the list. As described below, the mapping of operations to buttons 116 a-h can be determined by PMD 102. When a user presses one of buttons 116 a-h, accessory 104 can send to PMD 102 a signal indicating which of buttons 116 a-h was pressed. PMD 102 can interpret the signal and take appropriate action. The action may include updating the remote GUI image, starting or pausing playback, modifying a setting or instructing accessory 104 to modify a setting, etc.

Remote GUI image 111 on display 114 of accessory 104 can also include additional elements not found on native GUI image 101. For example, remote GUI image 111 includes GUI elements indicating a “Play” operation (element 119) and an “Exit” operation (element 121). Elements 119 and 121 are positioned next to buttons 116 a and 116 d, respectively, to indicate that the corresponding operations can be invoked by pressing the adjacent button. In this example, the user can press button 116 a to indicate that the currently selected track should be played. The user can press button 116 d to indicate that accessory 104 should exit the remote GUI mode, allowing the user to access other functionality (e.g., navigation, climate control, etc.). Interfaces for such other functionality might or might not also be controlled by PMD 102. In some embodiments, exiting the remote GUI mode does not disconnect accessory 104 from PMD 102; for example, PMD 102 and accessory 104 can continue playing a media track while the other functionality of accessory 104 is accessed.

FIG. 1C illustrates accessory 150 according to another embodiment of the present invention. Like accessory 104, accessory 150 can be an in-vehicle media control unit. Accessory 150 includes display 152 and docking bay 154 adapted to receive a PMD such as PMD 102 of FIG. 1A. In this example, docking bay 154 includes a connector 156 that mates with connector 110 of PMD 102, thereby allowing electrical signals to be transmitted back and forth between PMD 102 and accessory 150. In an alternative embodiment, PMD 102 and accessory 150 can each be equipped with a wireless communication interface (e.g., an interface implementing Bluetooth standards), thereby allowing the two devices to exchange information without a direct physical connection being made.

Display 152 of accessory 150 has a touch-sensitive overlay such that when a user touches a portion of display 152, the touched portion can be identified, e.g., using (x, y) pixel coordinates. A user can touch an element of the displayed GUI image to select an action to be taken, as suggested by hand 158. In other embodiments, the touch-sensitive overlay of display 152 can also detect finger motions such as dragging along the surface, or opening or closing fingers.

Like accessory 104 of FIG. 1B, when PMD 102 is connected to accessory 150, accessory 150 can enter a remote GUI operating mode and can display a remote GUI image 151 provided by PMD 102. Like remote GUI image 111 in FIG. 1B, remote GUI image 151 can be a modified version of native GUI image 101 of FIG. 1A. Remote GUI image 151 includes an album name (“ALBUM”) at the top and a listing of tracks beneath. A currently selected track (“Track 5”) is highlighted. Up and down arrows 153, 155 indicate that scrolling to view additional tracks is possible, and a slider element 157 indicates the approximate position of the currently selected track within the list of tracks. In this instance, the user can touch an area of the screen to select the corresponding action. Thus, for example, as shown in FIG. 1C, the user (hand 158) can touch down arrow 155 to advance the selection through the list (e.g., from “Track 5” to “Track 6”).

Remote GUI image 151 can also include additional elements not found on native GUI image 101. For example, remote GUI image 151 includes GUI elements indicating a “Play” operation (element 159), a “Back” operation (element 161), and an “Exit” operation (element 163). In this example, the user can touch “Play” element 159 to indicate that the currently selected track should be played. The user can touch “Back” element 161 to navigate backward in the database hierarchy (e.g., to a list of albums from which the currently displayed album was selected). The user can touch “Exit” element 163 to indicate that accessory 150 should exit the remote GUI mode, allowing the user to access other functionality (e.g., navigation, climate control, etc.). As noted above, interfaces for such other functionality might not be controlled by PMD 102. Also as noted above, exiting the remote GUI mode need not disconnect accessory 150 from PMD 102; for example, PMD 102 and accessory 150 can continue playing a media track while the other functionality is accessed.

As described below, the mapping of GUI elements to screen areas can be determined by PMD 102. When a user touches a portion of display screen 152, accessory 154 can simply send to PMD 102 a signal indicating which portion of the screen was touched (e.g., pixel coordinates of the touched location). PMD 102 can interpret the signal and take appropriate action. The appropriate action may include updating the remote GUI image, starting or pausing playback, modifying a setting or instructing accessory 104 to modify a setting, etc.

At different times, PMD 102 of FIG. 1A can be coupled to different accessories. Thus, for example, at one time PMD 102 can be coupled to accessory 104 of FIG. 1B and can provide a remote GUI suitable for use with an interface where the user input devices are buttons 116 a-h. At a different time, PMD 102 can be coupled to accessory 150 of FIG. 1C and can provide a remote GUI suitable for use with a touchscreen interface. Because the remote GUI is under the control of PMD 102, a user can interact with PMD 102 directly or through various accessories and experience a generally consistent interface from one configuration to the next. Such consistency can help to make the use of different interfaces, as well as the transition from one accessory to another, more intuitive for the user.

It will be appreciated that the systems of FIGS. 1A-1C are illustrative and that variations and modifications are possible. A variety of portable media devices may be used, not limited to PMD 102, and the native GUI may vary from one device to the next. For instance, some PMDs may provide touch-screen interfaces, graphic representations of content listings (e.g., incorporating images of album covers), animated GUI images, or other features not specifically illustrated herein. Some PMDs may also incorporate other functionality in addition to media asset storage, search, and playback. Examples include personal information management (e.g., calendar, contacts); telephony (e.g., via mobile phone network); Internet connectivity (e.g., via wireless communication protocols such as the IEEE 802.11 family of standards (also known as “WiFi”) and/or wireless data networks such as 3G or EDGE); maps and navigation; execution of application programs (including third-party application programs loaded onto the PMD by a user); and so on. The PMD may provide remote GUI interactivity for any or all of its functions, and the combination of functions available may vary depending on the accessory. (For example, to avoid driver distraction, it might be desirable to disable Internet browsing or video playback in a moving automobile.)

A remote GUI mode can be provided in a variety of accessories. For example, in addition to in-vehicle systems, a PMD interface with remote GUI can be provided in a console on an exercise machine (such as a treadmill, stationary bicycle, or the like), in an in-flight entertainment console of a commercial or private airplane, in a home entertainment system incorporating a video device such as a television (e.g., using a set top box or an integrated component of the video display device to provide an interface to the PMD), and so on.

FIG. 2 is a block diagram of system 200 according to an embodiment of the present invention. System 200 can include PMD 202 (e.g., implementing PMD 102 of FIG. 1A) and accessory 220 (e.g., implementing accessory 104 of FIG. 1B or accessory 150 of FIG. 1C).

PMD 202 in this embodiment can provide media player capability. PMD 202 can include processor 204, storage device 206, user interface 208, network interface 210 and accessory input/output (I/O) interface 214. Processor 204 in this embodiment can be a programmable processor that executes programs to implement operations such as playback of media tracks and browsing a database of stored media assets, as well as a native GUI to provide user control over the implemented operations. Processor 204 can also implement a remote GUI program that generates remote GUI images for accessory 220 and processes user input forwarded by accessory 220, as described below.

Storage device 206 may be implemented, e.g., using disk, flash memory, or any other non-volatile storage medium. In some embodiments, storage device 206 can store a database of media assets (also referred to herein as “tracks”), such as audio, video, still images, or the like, that can be played by PMD 202, together with metadata descriptive of each track. Metadata can include, e.g., a media type (audio track, video track, audio book, still image, etc.); an asset title; a name of an artist or performer associated with the asset; composer or author information; asset length; chapter information; album information; lyrics; information about associated artwork or images; description of the asset; and so on. Other information, including programs to be executed by processor 204 (e.g., a remote GUI program) and/or configuration information to be used in executing such programs (e.g., various display rules for a remote GUI image as described below), can be stored in storage device 206.

User interface 208 may include one or more input controls 207 such as a touch pad, touch screen, scroll wheel, click wheel, dial, button, keypad, microphone, or the like, as well as display screen 209. Other components, such as an audio output section (not explicitly shown) can also be included. A user can view native GUI images generated by processor 204 on display screen 209 and can operate input controls 207 based on the displayed image to invoke the functionality of PMD 202. Processor 204 can process the user input and take appropriate action, including updating the native GUI image on display screen 209. Thus, user interface 208 and processor 204 can provide a native GUI for PMD 202.

Network interface 210 can be operated under control of processor 204 to connect PMD 202 to various communication networks, including voice and data networks. For example, network interface 210 can provide local area network connections via WiFi, mobile telephony via suitable RF circuitry, access to wireless data networks including 3G and EDGE networks, personal area connections via Bluetooth, or the like. In some embodiments, network interface 210 can provide wired connections in addition to or instead of wireless connections.

Accessory I/O interface 214 can allow PMD 202 to communicate with various accessories. For example, accessory I/O interface 214 can support connections to such accessories as an in-vehicle media system or the like. In one embodiment, accessory I/O interface 214 includes a 30-pin connector corresponding to the connector used on iPod™ products manufactured and sold by Apple Inc. or one or more other connectors, such as a Universal Serial Bus (“USB”) or FireWire connector. Alternatively or additionally, accessory I/O interface 214 can include a wireless interface (e.g., Bluetooth or the like). Accessory I/O interface 214 can allow PMD 202 to communicate with accessory 220 or another accessory.

Accessory 220 includes controller 224, one or more input controls 222, display 232, PMD I/O interface 226, environmental and status input interface 228, and audio output section 230. Controller 224 can include, e.g., a microprocessor or microcontroller executing program code to perform various functions such as digital audio decoding, analog or digital audio and/or video processing, and the like. Input controls 222 can include, e.g., a touch pad, touch screen, scroll wheel, click wheel, dial, button, keypad, microphone, or the like. Display 232 can be used to present operational or control information as well as video content to the user; in some embodiments, display 232 can be implemented as a multi-screen display system, and the images shown on different screens might be the same or different. Thus, for example, one screen can be used for operational or control information while another screen is used for presenting video content. In still other embodiments, operational or control information can be overlaid or composed with video content, allowing a user to view both simultaneously on the same screen.

Accessory 220 can be operable in a “local GUI” mode as well as a remote GUI mode. In the local GUI mode, controller 224 can generate GUI images to be displayed on display 232 and can receive and process user input from input controls 222, thereby allowing a user to control various operations of accessory 220. In the remote GUI mode, GUI images can be generated by processor 204 of PMD 202, delivered via accessory I/O interface 214 and PMD I/O interface 226 to controller 224, and displayed on display 232. Controller 224 can detect user operation of input controls 222 and send corresponding signals to PMD 202 via PMD I/O interface 226 and accessory I/O interface 214. Processor 204 of PMD 202 can process the signals to determine what action the user has requested; depending on the user request, processor 204 can generate an updated remote GUI image to be displayed by display 232, generate other instructions to controller 224, or invoke other operations of PMD 202 (such as beginning or ending playback, searching the database of stored assets, etc.).

Audio output device 230, which can be implemented, e.g., as one or more integrated circuits, provides the capability to output audio. For example, audio output device 230 can include one or more speakers or driver circuits and connectors for external speakers, thereby enabling audio to be presented to a user. In one embodiment, controller 224 can receive audio signals from PMD 202 via PMD I/O interface 226 and can provide the signals with or without further processing to audio output device 230; audio output device 230 can transform the signals as appropriate for presentation to the user.

Environmental and status input interface 228 can include communication pathways to other systems of the equipment in which accessory 220 is installed, allowing these systems to provide accessory 220 with information about the operating environment and/or status. For example, if accessory 220 is installed in an automobile, environmental status input interface 228 may receive information indicating whether the automobile's headlights are on or off, what gear the vehicle is currently in, whether a parking brake is engaged, current vehicle speed, etc. If accessory 220 is installed in an exercise machine, environmental status input interface 228 may receive information indicating whether the machine is in use and information about the current status of a workout when one is in progress. Accessory 220 can provide this information to PMD 202, and PMD 202 can use the information to customize the remote GUI images and functionality to the operating environment, as described below.

Accessory 220 can be any accessory that provides a display and one or more associated user input controls. Examples include in-vehicle media units that can be mounted, e.g., in a dashboard or seat back, consoles that may be provided on exercise equipment, airplane in-flight entertainment systems (e.g., mounted in a seatback, armrest, or console unit), home entertainment systems, and so on. In one embodiment, PMD I/O interface 226 includes a 30-pin connector that mates with the connector used on iPod™ products manufactured and sold by Apple Inc. PMD I/O interface 226 can also include other types of connectors, e.g., Universal Serial Bus (USB) or FireWire connectors. Alternatively, PMD I/O interface 226 can include a wireless interface (e.g., Bluetooth or the like).

It will be appreciated that the system configurations and components described herein are illustrative and that variations and modifications are possible. The PMD and/or accessory may have other capabilities not specifically described herein. For example, the PMD can include any combination of computing and/or communication functionalities in addition to media playback capability. Examples of other functionalities that can be provided by a PMD include personal information management (e.g., calendar, contacts); telephony (e.g., via mobile phone network); Internet connectivity (e.g., via wireless communication protocols such as WiFi and/or wireless data networks such as 3G or EDGE); maps and navigation (e.g., using a Global Positioning System (“GPS”) receiver; execution of application programs (including third-party application programs that may be loaded onto the PMD by a user); and so on.

Further, while the PMD and accessory are described herein with reference to particular blocks, it is to be understood that these blocks are defined for convenience of description and are not intended to imply a particular physical arrangement of component parts. Further, the blocks need not correspond to physically distinct components. Embodiments of the present invention can be realized in a variety of devices including electronic devices implemented using any combination of circuitry and software.

Accessory I/O interface 214 of PMD 202 and PMD I/O interface 226 of accessory 220 allow PMD 202 to be connected to accessory 220 and subsequently disconnected from accessory 220. As used herein, PMD 202 and accessory 220 are “connected” whenever a communication channel between accessory I/O interface 214 and PMD I/O interface 226 is open and are “disconnected” whenever the communication channel is closed. Connection can be achieved by physical attachment (e.g., between respective mating connectors of PMD 202 and accessory 220), by an indirect connection such as a cable, or by establishing a wireless communication channel. Similarly, disconnection can be achieved by physical detachment, disconnecting a cable, powering down accessory 220 or PMD 202, or closing the wireless communication channel. Thus, a variety of communication channels may be used, including wired channels such as USB, FireWire, or universal asynchronous receiver/transmitter (“UART”), or wireless channels such as Bluetooth. In some embodiments, PMD 202 can be connected to multiple accessories concurrently using any combination of wired and/or wireless communication channels.

Regardless of the particular communication channel, as long as PMD 202 and accessory 220 are connected to each other, the devices can communicate by exchanging commands and data according to a protocol. The protocol defines a format for sending messages between PMD 202 and accessory 220. For instance, the protocol may specify that each message is sent in a packet with a header and an optional payload. The header provides basic information (e.g., a start indicator, length of the packet, and a command to be processed by the recipient), while the payload provides any data associated with the command; the amount of associated data can be different for different commands, and some commands may provide for variable-length payloads. In some embodiments, the commands may be defined such that a particular command is valid in only one direction. The packet can also include error-detection or error-correction codes as known in the art.

The protocol can define a number of “lingoes,” where a “lingo” is a group of related commands that can be supported (or unsupported) by various classes of accessories. In one embodiment, a command can be uniquely identified by a first byte identifying the lingo to which the command belongs and a second byte identifying the particular command within the lingo. Other command structures may also be used. It is not required that all accessories, or all PMDs to which an accessory can be connected, support every lingo defined within the protocol.

In some embodiments, every accessory 220 and every PMD 202 that are designed to be interoperable with each other support at least a “general” lingo that includes commands common to all such devices. The general lingo can include commands enabling the PMD and the accessory to identify and authenticate themselves to each other and to provide general information about their respective capabilities, including which (if any) other lingoes each supports. The general lingo can also include authentication commands that the PMD can use to verify the purported identity and capabilities of the accessory (or vice versa), and the accessory (or PMD) may be blocked from invoking certain commands or lingoes if the authentication is unsuccessful.

A command protocol supported by PMD 202 and accessory 220 can include a “remote GUI” lingo (or other group of commands) that can be used to communicate commands and data related to permitting a user to control the operation of PMD 202 via a remote GUI provided on accessory 220. The remote GUI lingo can include commands that accessory 220 can send to PMD 202 to provide information about the configuration of display 232 and input controls 222, as well as environmental information (such as where accessory 220 is installed, operational status of a vehicle or other equipment in or on which accessory 220 is installed, etc.). The remote GUI lingo can also include commands used by PMD 202 to deliver GUI image data to accessory 220 and commands used by accessory 220 to forward user input signals to PMD 202. Examples are described below.

Commands that can be used to implement a remote GUI according to an embodiment of the invention will now be described. In one embodiment, the commands can include commands usable to provide a PMD with information about the configuration of an accessory's display device and user input control(s). The commands can also include commands usable to provide the PMD with information about the environment in which the accessory operates and any special requirements of the accessory, such as logos or other content to be included in the remote GUI image. The commands can also include a command used to send remote GUI image data to the accessory and a command used to send user input information to the PMD.

FIG. 3 is a table 300 listing commands that can be used to implement a remote GUI according to an embodiment of the present invention. For each command, the direction and payload are indicated. “Direction” refers to whether the command is sent from the PMD to the accessory (denoted “P A”) or vice versa (denoted “A P”). “Payload” refers to any data or other parameters associated with the command.

In some embodiments, a SetDisplayInfo command can be sent by accessory 220 to PMD 202 to provide information about display 232. In one embodiment, the information can include any or all of: the display dimensions (e.g., in pixels or inches or both) of a display device, color depth information for the display device (e.g., whether the display is color or black and white, the number of distinct color values supported, etc.); the display format of the display device (e.g., analog or digital input and signal formats); and the refresh rate of the display device. In some embodiments, accessory 220 may provide multiple display devices, and the information provided to PMD 202 may include the number of display devices as well as separate configuration information for each display device.

In some embodiments, a SetDisplayRules command can be sent by accessory 220 to PMD 202 to specify desired parameters for remote GUI images. For example, in some embodiments, accessory 220 may be in an environment (e.g., an automobile) where safety concerns indicate that displayed information should be sized and organized such that it can be quickly and easily read by a user (e.g., a driver). Accordingly, in some embodiments, accessory 220 can provide display “rules,” such as a minimum character size (in absolute dimensions such as inches or centimeters or in pixels), minimum character pitch or space between lines (also in absolute dimensions or pixels), maximum number of lines of text per screen, preferred font, minimum size of graphical objects (e.g., icons, streets on a map), or the like. PMD 202 can apply these rules in generating remote GUI images for accessory 220.

In some embodiments, e.g., for automobiles, display rules can be based on national or regional safety regulations. PMD 202 can be programmed with a lookup table or other data structure that associates applicable display rules with various nations or regions, and accessory 220 can provide a nation or region identifier via the SetDisplayRules command. In response to receiving a nation or region identifier, PMD 202 can look up the applicable display rules.

In some embodiments, a SetControlInfo command can be sent by accessory 220 to PMD 202 to provide information about the type, number and location of user input controls 222. In one embodiment, the command can first identify the number of controls. Then, for each control, the command can identify the type (e.g., button, knob, touchscreen) and approximate location of the control. The command can also provide additional parameters describing the control. For example, in the case of a touchscreen, the command can specify the cell size or resolution of the touchscreen.

In some embodiments, a SetEnvInfo command can be sent by accessory 220 to PMD 202 to provide information about the environment in which accessory 220 operates. For instance, the environmental information can include information as to where accessory 220 is installed, e.g., vehicle dashboard, airplane in-flight entertainment system; exercise equipment console, home entertainment system, etc.

In some embodiments, a SetEnvImage command can be sent by accessory 220 to PMD 202 to provide an image element that can be included in a remote GUI image. For example, the image element might be a logo associated with the manufacturer or provider of accessory 220 (or of a vehicle or other equipment in which accessory 220 is installed). As described below, PMD 202 can reserve an area of the remote GUI image for displaying an accessory-supplied image.

In some embodiments, a SetStatusInfo command can be sent by accessory 220 to PMD 202 to provide information about the status of the operating environment. For example, if accessory 220 is installed in an automobile dashboard, status information may include information such as whether the automobile is in motion (or in gear); whether it is day or night (e.g., whether the automobile's headlights are off or on); whether navigational route guidance is in progress; etc. If accessory 220 is installed in an exercise machine such as a treadmill, status information may include information such as whether the machine is currently in use as well as workout data such as elapsed or remaining time, calories burned, heart rate, current speed, or the like. As described below, status information provided by the accessory can be used by PMD 202 to augment the remote GUI images with status information, to adjust the appearance of the remote GUI images based on the current status, and/or to limit access to certain features (such as video playback) in a status-dependent manner.

In some embodiments, a RemoteGUIImageData command can be sent by PMD 202 to accessory 220 to deliver pixel data for a remote GUI image to accessory 220. The command can include pixel data for a portion or all of display 232. In some embodiments, a command packet may have a maximum size, which can limit the amount of pixel data that can be sent with a single RemoteGUIImageData command. In this case, PMD 202 can use multiple RemoteGUIImageData commands to send the pixel data; each command may include a parameter identifying the portion of the display to which the pixel data applies. Any format suitable for sending pixel data, including compressed formats, can be used. In other embodiments, accessory I/O interface 214 of PMD 202 can incorporate a video output interface, which can be analog or digital, and the remote GUI image can be delivered to accessory 220 through the video output interface rather than by sending commands.

In some embodiments a ProcessUserInput command can be sent by accessory 220 to PMD 202 to indicate the detection of user input in response to a remote GUI image. The command can include data indicating, e.g., which user control was operated and, if applicable, what operation was performed. For instance, for accessory 104 of FIG. 1B, the ProcessUserInput data can indicate which one of buttons 116 a-h was pressed. For accessory 150 of FIG. 1C, the ProcessUserInput data can indicate pixel coordinates of a location on the screen that was touched by the user. For a user input device that can be manipulated in multiple ways (e.g., turning a knob either clockwise or counterclockwise or dragging a finger across a suitably configured touchscreen), the ProcessUserInput data can also indicate which manipulation of the input device was detected.

In some embodiments, an EnterRemoteGUIMode command can be sent from accessory 220 to PMD 202 (or vice versa) to initiate remote GUI mode operation, and an ExitRemoteGUIMode command can be sent from PMD 202 to accessory 220 (or vice versa) to terminate remote GUI mode operation.

FIG. 4 is a table 400 listing commands that can be used to implement a remote GUI according to another embodiment of the present invention. As in table 300, for each command the direction and payload are indicated.

In some embodiments, an AccessorySettings command can be sent by accessory 220 to PMD 202 to provide information about its characteristics. The AccessorySettings command can be a general-lingo command for providing information about the accessory's capabilities, preferences, and/or settings; in some embodiments, this command is also usable to send information unrelated to remote GUI operations. The payload of the AccessorySettings command can include a token identifying the type of information being provided (e.g., information about display capabilities, information about audio capabilities, etc.) and a descriptor associated with the token that carries the specific information. For example, in the case of a display token, the associated display descriptor can include information indicating properties of the accessory's display screen. In one embodiment, properties can include the vertical and horizontal physical screen size (e.g., in inches or centimeters); the vertical and horizontal screen resolution (e.g., in number of pixels); the vertical and horizontal dimensions of the portion of the screen allocated to the remote GUI (e.g., in number of pixels); the screen's color depth (e.g., in number of bits or simply an indicator of whether the screen is color or black and white); the screen's gamma (color correction) factor; and other features such as whether the display is touch-sensitive, touch resolution (e.g., number of cells, cell size, size of touch-sensitive area).

In some embodiments, the display descriptor can also include other information, such as the video signal format used by the accessory (e.g., NTSC, PAL, etc.); video connection type (e.g., composite video, S-Video, component video, etc.); video scan mode (e.g., interlaced or progressive); screen aspect ratio (e.g., 4:3 full-screen or 16:9 wide-screen); and so on. In other embodiments, some or all of this additional display information can be provided using, e.g., a SetVideoPreferences command of the general lingo. The SetVideoPreferences command may also provide the ability to adjust settings related to playback of video content but unrelated to the remote GUI, such as whether to show or hide captions and subtitles when playing videos, or whether the video image should be stretched to fill the screen or leave black bands. (As described above, the dimensions of the remote GUI image can be specified using the AccessorySettings command and may be unaffected by whether image stretching is selected for video playback.)

Those skilled in the art will appreciate that some combinations of preferences may cause errors; for example, selection between progressive and interlaced scan modes may not be permitted for composite video or S-video connections (which support only interlaced scan mode). If an error occurs, the PMD may send an error message as a command to the accessory.

In some embodiments, the AccessorySettings command can be sent with a “display rules” token, indicating that the associated descriptor identifies display rules, or desired parameters for remote GUI images. As described above, display rules can be based on national or regional safety standards for particular types of accessories, and the display rules token can simply provide an identifier of the applicable nation or region. In other embodiments, the display rules descriptor can provide specific display rules such as minimum character size, minimum line spacing or pitch, maximum number of lines per screen, preferred font, minimum size of graphical objects, etc.

In some embodiments, the AccessorySettings command can also be used to provide information about user input controls that are to be associated with the remote GUI. For example, a token associated with input control information can be defined. The associated descriptor can contain information about the controls, such as the number of controls, the type of each control (e.g., rotational, button, or touchscreen), the approximate location of each control, control parameters (e.g., touchscreen cell size or touch resolution parameters) etc., similarly to the SetControlInfo command described above. The accessory can also assign each control a unique identifier and include the assigned identifier in the control descriptor. They accessory can subsequently use the assigned identifier to specify to the PMD which control was operated.

In some embodiments, PMD 202 may be able to selectively expose various content or functionality to accessory 220 via the remote GUI. For example, as described above PMD 202 can support multiple functionalities such as audio playback, video playback, still image browsing and playback, mobile telephony, e-mail, web browser, personal information storage and retrieval, execution of various third party application programs that may be stored in storage device 206, GPS navigation capability, and so on. Further, a particular PMD 202 can be part of a family of media and communication devices, each of which may support different combinations of functionalities. In some embodiments, one PMD model might provide only audio playback while a second model provides audio and video playback, a third model provides audio and video playback as well as mobile telephony, and so on. Thus, which functionalities are available may vary from one PMD to the next, and which of the available functionalities should be exposed via the remote GUI may depend in part on the accessory and its operating environment.

To allow the accessory to control which of the available functionalities are or are not exposed via the remote GUI, some embodiments provide “options” commands, such as the GetPMDOptions, RetPMDOptions, and SetPMDOptions commands of table 400. The GetPMDOptions command can be sent by accessory 220 to PMD 202 to request information about which functionalities are available from PMD 202. The payload can include a selector, allowing the accessory to indicate whether the PMD should respond by listing all available functionalities (i.e., all functionalities that the PMD supports and is capable of exposing via the remote GUI) or only those functionalities that are active (i.e., currently selected for exposure via the remote GUI).

The RetPMDOptions command can be sent by PMD 202 to accessory 220 in response to the GetPMDOptions command. The payload can provide a list of available or active functionalities, depending on the selector in the GetPMDOptions command. In one embodiment, the list can be implemented as a bitmask with a different bit assigned to each functionality that could be exposed via the remote GUI if a particular PMD supports it. For instance, bits can be assigned to audio playback, video playback, still image browsing, web browsing, GPS navigation, telephone, and so on. If the GetPMDOptions selector requests a list of available functionalities, PMD 202 can set the bits to indicate which functionalities are available. If the GetPMDOptions selector requests a list of active functionalities, PMD 202 can set the bits to indicate which functionalities are currently active. In other embodiments, the list can be implemented using other data structures. For example, a unique byte code can be associated with each functionality, and the payload of the RetPMDOptions command can include a list of byte codes identifying available or active functionalities.

The SetPMDOptions command can be sent by accessory 220 to PMD 202 to specify the functionalities that should be made active. The payload can be a bitmask, e.g., using the same mapping of bits to functionalities as the RetPMDOptions command, and accessory 220 can set the bits according to whether a particular functionality should or should not be active. Thus, for example, if accessory 220 is installed in a vehicle, it may be desirable to expose only functionalities that will not unduly distract the driver, such as audio but not video playback, or navigation but not web browsing. Accessory 220 can set the bitmask appropriately for the desired behavior. Alternatively, in embodiments where byte codes are associated with each functionality, accessory 220 can send a list of the byte codes associated with the functionalities that should be active. In some embodiments, if accessory 220 requests a functionality that a particular PMD 202 does not support or cannot expose via the remote GUI, PMD 202 can respond with an error message.

PMD 202 can use the payload of the SetPMDOptions command in generating remote GUI images. For example, menus presented in a remote GUI image may include only items associated with active functionalities, or items associated with inactive functionalities may appear in darkened, grayed-out or other de-emphasized form, indicating to the user that they are not available. In some embodiments, if accessory 220 does not send a SetPMDOptions command, PMD 202 can expose a default set of functionalities. For example, all available functionalities can be exposed by default, or the default set can be limited to a minimal set of functionalities (e.g., only audio playback).

In some embodiments, accessory 220 can send the SetPMDOptions command at any time, including during remote GUI operation, to dynamically change the set of active functionalities. For instance, if accessory 220 is installed in an automobile, video playback or web browsing functionality might be inactive while the automobile is being driven and active while the automobile is parked. Whether an automobile is parked can be detected, e.g., by detecting whether an automatic transmission is shifted into “Park” or whether the automobile's parking brake is engaged. In response to detecting a transition into or out of a parked state, accessory 220 can send a new SetPMDOptions command to change the set of active functionalities.

The BrightnessAdjust command can be sent by accessory 220 to PMD 202 to signal a change in display brightness. The payload can be an indicator of the desired brightness. In one embodiment, the payload corresponds to a gain setting for a digital-to-analog converter used by PMD 202 to generate analog video output signals; other indicators of brightness can also be used. The BrightnessAdjust command can be used, e.g., in vehicles that have panel brightness controls, allowing PMD 202 to adjust the brightness of the remote GUI image in coordination with adjustments to brightness of other lights on the panel. Other commands related to adjusting display parameters can also be provided.

The SetStatusInfo command can be similar to the SetStatusInfo command described above with reference to FIG. 3. This command can be sent by accessory 220 to PMD 202 to provide information about changes in the status of the operating environment, and any of the status information described above can be provided.

In some embodiments, additional status changes can be provided using the SetStatusInfo command. For example, accessory 220 can be implemented in a head unit (e.g., in an automobile) that is capable of receiving video and/or audio input from different sources. Video input can be received, from PMD 220 or from a different source such as a built-in GPS navigation unit or DVD player. Similarly, audio input can be received from PMD 220 or from a different source such as a built-in radio receiver or CD or DVD player. A user may be able to operate a control of accessory 220 to change the audio and/or video source at any time, regardless of whether PMD 202 is currently providing a remote GUI. Accordingly, the SetStatusInfo command can be used to signal when the accessory's audio source selection changes to or from PMD 202 and/or when the accessory's video source selection changes to or from PMD 202. Depending on implementation, a particular PMD 202 might or might not act on the status-change information provided by the accessory; however, the accessory can always send the SetStatusInfo command in response to any status-change event regardless of whether or how a particular PMD 202 might respond.

In the embodiment described above with reference to FIG. 3, accessory 220 can communicate any type of user input to PMD 202 using a single ProcessUserInput command. Alternatively, as shown in FIG. 4, different commands can be associated with different types of user input controls. For example, depending on the type of input device that is operated, accessory 220 can send a ButtonInput command, a RotationInput command, or a TouchInput command. In some embodiments, accessory 220 can continue to send the appropriate input command at regular intervals (e.g., 20 ms, 50 ms, or the like) for as long as the user continues to operate a particular control.

The ButtonInput command can be used to communicate information about the operation of a control button to PMD 202. In some embodiments, as described above, accessory 220 can provide identifying information about each button in advance, e.g., using the AccessorySettings or SetControlInfo command as described above. In such embodiments, the ButtonInput command can simply include an identifier of the button that is activated, or a bitmask indicating which of the buttons are activated at the time of the ButtonStatus command. As noted above, the ButtonInput command can be sent at regular intervals for as long as a user continues to hold one or more buttons down. When all buttons are released, a final ButtonStatus command can be sent with a payload indicating that all buttons have been released.

In other embodiments, accessory 220 is not required to provide information about its input controls in advance of use. Instead, the accessory can internally map its controls to a set of generic GUI navigation buttons, e.g., Up, Down, Left, Right, Select, and Menu. In this case, the ButtonStatus command can be implemented with a “control-source” parameter that identifies the location of the active button (or other control) and a bitmask associated with the generic GUI navigation buttons. For instance, in one embodiment where accessory 220 is an automobile head unit, the control-source parameter can indicate where in the automobile the button is located (e.g., on the dashboard, on the steering wheel, on the center console); this parameter may identify a group of buttons (or other controls) rather than a single button. In this embodiment, accessory 220 determines the mapping of controls to the GUI navigation buttons of the bitmask and sets the appropriate bit (or bits) in the bitmask to indicate the control operation.

The RotationInput command can be used to communicate information about the operation of a rotational input control such as a free wheel or jog wheel. The payload can include a control-source parameter that identifies which rotational control was operated and additional parameters describing the operation.

The control-source parameter can be defined in various ways. In embodiments where accessory 220 provides information about its controls in advance of their use (e.g., using the AccessorySettings or SetControlInfo command as described above), the control-source parameter can be the control identifier assigned by accessory 220. In other embodiments, accessory 220 is not required to provide information about the controls in advance of use. In such embodiments, the control-source parameter can simply identify the approximate location of the control that was operated. For instance, in one embodiment where accessory 220 is an automobile head unit, the control-source parameter can indicate where in the automobile the rotational control is located (e.g., on the dashboard, on the steering wheel, on the center console) and the type of control (e.g., free wheel or jog wheel).

The type of operation can be characterized using additional parameters. For example, the direction of rotation (e.g., left/right, or up/down) can be indicated by a parameter. The particular action, e.g., whether the rotation has ended or is in progress, can also be indicated. For jog wheels, rotation can be considered as “in progress” for as long as the user continues to hold the wheel away from the home position even if the control is not actually moving. Alternatively, a separate action type can be defined to indicate that the user is holding the wheel in a position corresponding to the indicated direction of rotation.

In some embodiments, the amount of rotation of a free wheel or jog wheel during a relevant time interval can be measured and reported. For instance, some knobs provide a series of detents, and the amount of rotation can be reported as the number of detents traversed as a fraction of the total number of detents available. Alternatively, the amount of rotation can be measured in degrees or the like.

As noted above, the RotationInput command can be sent at intervals while the user continues to operate the control. Where the amount of rotation is reported, each instance of the command can report the amount of rotation since the last command was sent. When the rotational action ends, accessory 220 can send a final RotationInput command indicating that the operation has stopped.

The TouchInput command can be used to communicate information about the operation of a touch-sensitive input control. The payload can include a control-source parameter identifying which control was operated and additional parameters describing the operation.

As with other input commands described herein, the control-source parameter can be defined in various ways. For example, in embodiments where accessory 220 provides information about the controls in advance of use (e.g., using the AccessorySettings or SetControlInfo command as described above), the control-source parameter can be the control identifier assigned by accessory 220. In other embodiments, accessory 220 is not required to provide information about the controls in advance of use. In such embodiments, the control-source parameter can simply identify the approximate location of the control that was operated. For instance, in one embodiment where accessory 220 is an automobile head unit, the control-source parameter can indicate where in the automobile the touch-sensitive control is located (e.g., on the dashboard, on the center console) as well as the type of touch-sensitive input control (e.g., single-touch or multitouch).

The type of operation can be characterized, e.g., by coordinates indicating the location that was touched. In one embodiment, coordinates can be specified using position indexes in the horizontal and vertical directions (e.g., starting from top left of the touch-sensitive area), and accessory 220 can provide the maximum index along with the actual index of the touched location. Alternatively, the touched location can be identified using pixel coordinates, physical measurements (e.g., inches from the screen's edge), or the like. In some embodiments using a multitouch input control, accessory 220 can interpret a user action as a “gesture,” e.g., tap, pinch, swipe, etc.; and the type of operation can be characterized by the gesture type as well as coordinates touched, speed, number of fingers used, and the like.

As with other input commands described herein, accessory 220 can send TouchInput commands at regular intervals as long as a touch operation continues. When the operation ends, accessory 220 can send a final TouchInput command indicating that the operation has stopped.

The EnterRemoteGUIMode and ExitRemoteGUIMode commands described above can allow accessory 220 to switch PMD 202 into or out of remote GUI mode. In some embodiments, PMD 202 may have more than two user interface (“UI”) modes. For example, PMD 202 can have a standard operating mode in which it presents its native GUI on its own display, a remote GUI mode in which it delivers GUI images to accessory 220, and an external UI mode in which an accessory provides a local GUI for controlling PMD 202. In some embodiments, PMD 202 can disable its native GUI when operating in remote GUI mode or external UI mode; in other embodiments, PMD 202 can simultaneously provide a native GUI and a remote GUI or external UI.

Where more than two UI modes are provided, it can be useful for accessory 220 to determine and select the desired mode. Accordingly, the commands in table 400 include a GetUIMode command, a RetUIMode command, and a SetUIMode command. Accessory 220 can send the GetUIMode command to determine the current UI mode, and PMD 220 can respond with the RetUIMode command, whose payload includes an identifier of the current UI mode. To change the UI mode, accessory 220 can send the SetUIMode command with a payload identifying the desired mode.

It will be appreciated that the commands described herein are illustrative and that variations and modifications are possible. Commands from tables 300 and 400 can be used in combination with each other, and other commands may be added or substituted. In some embodiments, an acknowledgement (Ack) command can be sent by the PMD in response to any command from the accessory that does not require another responsive command. The Ack command can have a payload including a status indicator, which can be used to communicate errors.

In some embodiments, PMD 202 can maintain a list of configuration data for known remote-GUI-enabled accessories, e.g., in storage device 206. Each configuration can be associated with a particular accessory identifier, such as manufacturer plus model name, an arbitrarily assigned code, or the like. Instead of sending configuration information commands as described above, accessory 220 can send an identification command that provides the accessory identifier. PMD 202 can then access the stored configuration data for the accessory. This can result in faster and more efficient setup.

In other embodiments, the first time a particular accessory such as accessory 220 connects to PMD 202, the accessory can use the SetDisplayInfo and SetControlInfo commands described above to establish its configuration. PMD 202 can then assign the accessory a unique identifier, provide the assigned identifier to the accessory, and store the configuration information in storage device 206 in association with the identifier. On subsequent reconnections, the accessory can send an identification command with the unique identifier to PMD 202, and PMD 202 can access the stored configuration information.

Other commands may also be included, such as commands associated with identifying PMD 202 to accessory 220 (or vice versa), authenticating accessory 220 to PMD 202 (or vice versa), and providing additional information about the capabilities of PMD 202 to accessory 220. For example, using appropriate commands, accessory 220 can determine the specific model and/or serial number of PMD 202, whether a particular PMD 202 supports a remote GUI at all, and (where there are multiple possible versions of the remote GUI functionality), which version of remote GUI functionality the particular PMD 202 supports. Accessory 220 can use this information in determining whether to enter remote GUI mode with a particular PMD 202.

In any of the above-described commands, information can be sent as a structured data field, e.g., with certain bytes associated with certain information types. Alternatively, the command may include a bitmask parameter used to identify the type of information being delivered, and the data can be interpreted by the recipient in accordance with the bitmask.

Further, the set of commands can also include commands sent by PMD 202 to request any of the available information types, as well as commands sent by PMD 202 to acknowledge receipt of the information-providing commands from accessory 220.

In some embodiments, some information can be sent by accessory 220 either in response to a request from PMD 202 or without waiting for a request, e.g., in response to changed conditions. For instance, if accessory 220 is installed in a vehicle with automatic transmission, accessory 220 might send a SetStatusInfo command when it detects that the vehicle is shifted into or out of Park. Alternatively, accessory 220 might monitor the vehicle's speed and send a SetStatusInfo command reporting the current speed, either periodically or when it detects that the vehicle's speed crosses above or below a predetermined threshold. In one embodiment, video operation can be enabled or disabled depending on whether the vehicle's speed is above or below the threshold; the threshold can be set to zero or a slow speed such as 5 miles per hour.

Depending on implementation, either the accessory or the PMD can determine which functionalities of the PMD are to be exposed through the remote GUI. As described above, the accessory can send commands to select the functionality that should be presented, or the PMD can select functionality based on the current status of the accessory.

FIG. 5 is a flow diagram of process 500 that can be used to provide a remote GUI for PMD 202 on accessory device 220 according to an embodiment of the present invention. Process 500 starts (block 502) when accessory 220 becomes connected to PMD 202. At block 504, accessory 220 is identified and authenticated. Conventional techniques for identifying and authenticating an accessory, e.g., by exchanging commands and associated data, can be used. Block 504 can also include determining whether remote GUI mode is to be entered; for example, accessory 220 can send the EnterRemoteGUIMode command or the SetUIMode command described above.

At block 506, accessory 220 can provide configuration, environment and/or status information to PMD 202. In one embodiment, any combination of the SetDisplayInfo, SetDisplayRules, SetControlInfo, SetEnvInfo, AccessorySettings, and SetStatusInfo commands described above can be used. Accessory 220 can also provide an accessory-specific (or environment-specific) image element to PMD 202, e.g., using the SetEnvImage command described above. In some embodiments, some or all of the configuration and environment information for accessory 220 can be pre-stored in PMD 202 as described above, and block 506 may include PMD 202 using the accessory identification obtained during block 504 to access the pre-stored configuration and environment information. Accessory 220 can also supplement or override any pre-stored information with new information using the commands described above.

At block 508, PMD 202 generates an initial remote GUI image using the information provided at block 506. In one embodiment, PMD 202 can apply various rules (including display rules received from accessory 220) to adapt the native GUI image to the configuration of accessory 220 and/or to the status or environment of accessory 220. Such rules can be incorporated into a control program executed by processor 204 to generate remote GUI images.

For instance, the remote GUI can be adapted to the particular configuration of the accessory's display 232. For example, the size (in pixels or physical dimensions) of accessory display 232 of FIG. 2 (or the portion thereof allotted to the remote GUI) might be different from the size of PMD display 209. PMD 202 can modify the native GUI image by changing the size of image elements, changing the number of elements displayed, or both. Further, the aspect ratio (height to width) of accessory display 232 may be different from that of PMD display 209, and PMD 202 may arrange the elements of the remote GUI image to optimize use of the available space. In still another example, the color depth of accessory display 232 might also be different from that of PMD display 209, and PMD 202 can adjust the color settings for various image elements to produce a visually pleasing appearance.

In some embodiments, the remote GUI can be adapted to conform to display rules specified by accessory 220. For example, a display rule may specify a minimum allowable character size, spacing between lines of text, minimum size and/or spacing for graphical objects (e.g., icons) or the like. PMD 202 can modify the native GUI image to conform to the design rules. This can include changing the amount and/or arrangement of information included in a single remote GUI image. Examples are described below.

Additionally, as noted above, accessory 220 may supply an image element to PMD 202. PMD 202 can determine a size and position for the accessory-supplied image element within the remote GUI image. The element might be small, such as a logo in a corner of the display area, or it can be larger as desired.

In embodiments where accessory 220 provides information about its input controls 222 in advance of use, PMD 202 can adapt the remote GUI image to the particular configuration of the accessory's user input controls 222. For example, if accessory input control 222 provides a touch screen (e.g., as shown in FIG. 1C), GUI elements can be placed anywhere within the active area of the touch screen. If accessory input control 222 provides an array of buttons (e.g., as shown in FIG. 1B), active GUI elements can be placed near the button that is mapped to that element. PMD 202 can determine the mapping of GUI elements to buttons or other input controls and arrange the elements accordingly within the display area.

As described above, in some embodiments, accessory 220 need not provide any configuration information for input controls 222 in advance of their use. In such embodiments, PMD 202 can configure the remote GUI image without regard to the physical location of input controls 222. The remote GUI image can be organized to facilitate intuitive navigation with up/down and/or left/right buttons, e.g., by arranging selectable items in a list or grid and providing a cursor that visually distinguishes one item as being the current selection (i.e., the item that will be activated if the user presses a select button).

In some embodiments, PMD 202 can adapt the remote GUI to the environment of accessory 220. For example, if accessory 220 is incorporated into a dashboard console for an automobile, it may be desirable to adapt the remote GUI image for ease of use by a driver. Accordingly, PMD 202 can select different fonts or font sizes to make remote GUI elements and displayed information larger and easier to read. PMD 202 may also simplify the GUI, e.g., omitting animations or reducing the number and/or complexity of GUI elements on a single screen, to minimize driver distraction. In contrast, for an accessory that is mounted on an exercise machine, user distraction may be less of a concern, and PMD 202 can provide complex or animated remote GUI images.

In another example, the native GUI of PMD 202 may use a light background with dark text and highlighting. This can provide good visibility in daylight, but when driving at night, the resulting brightness might be distracting. In some embodiments PMD 202 can adapt the color scheme depending on whether accessory 220 is in day or night mode—e.g., selecting bright text and dark backgrounds for nighttime use, or dark text and bright backgrounds for daytime use. Day or night mode can be selected based on status information provided by accessory 220; for example, as noted above accessory 220 can use a SetStatusInfo command to indicate when vehicle headlights are turned on or off, and PMD 202 can switch to day night or day mode depending on the state of the headlights. In other embodiments, the remote GUI can incorporate a user-settable option to select day or night mode. In still other embodiments, PMD 202 can select between day or night mode based on a BrightnessAdjust command received from accessory 220; brightness below (or above) a certain threshold can be interpreted as a request for night (or day) mode.

As another example, PMD 202 may use environment and/or status information to determine which options or functionalities should be made available (exposed) in the remote GUI. For example, PMD 202 may provide video playback capability and may be able to send video content to accessory 220 for display. But playing video on a console visible to the driver of a moving automobile is hazardous. To mitigate this hazard, accessory 220 can provide status information indicating, e.g., whether the automobile is in motion (or in gear) at a given time. PMD 202 can use this status information to determine whether it is safe to allow video playback. If not, video playback options can be omitted from the remote GUI image or shown in a disabled state. Thus, for instance, PMD 202 can enable video playback only when an automobile is in “Park,” only when the parking brake is engaged, or only when the vehicle's speed is below a particular threshold (such as 5 miles per hour). Similarly, any other functionalities supported by PMD 202 can be selectively hidden or exposed in response to environmental status information.

As yet another example, in some embodiments, accessory 220 can specify the functionalities or options that should be made available in the remote GUI, e.g., using the SetPMDOptions command described above. In generating the remote GUI image, PMD 202 can limit the elements displayed to those that correspond to active functionalities or options. Inactive functionalities or options can be omitted from the remote GUI image entirely or included with a visual indication signifying that they are inactive (e.g., image elements corresponding to inactive functionalities can be grayed-out, darkened, lightened, or otherwise visually de-emphasized).

In some embodiments, PMD 202 can incorporate status information into the remote

GUI. For example, if accessory 220 is incorporated into a console for an exercise machine, accessory 220 can provide PMD 202 with information about a workout in progress as noted above. PMD 202 can incorporate this information into the remote GUI image, allowing a user to monitor the progress of his or her workout while manipulating the remote GUI or playing video content. In embodiments where accessory 220 provides an image element (such as a logo), PMD 202 can incorporate the image element into the remote GUI. For example, PMD 202 may be programmed to reserve a portion of a remote GUI image for an accessory-supplied image element and may insert the accessory-supplied element into the reserved portion in any or all remote GUI images. PMD 202 can resize the accessory-supplied image element as needed to make it fit within the reserved area. (If the accessory does not supply an image element, the reserved portion can be left blank or filled with a default image element.)

Referring again to FIG. 5, at block 510, PMD 202 can send the remote GUI image to accessory 220. For example, PMD 202 can send the image using an analog or digital video output interface provided by accessory I/O interface 214 and PMD I/O interface 226 of FIG. 2. (The same video interface can also be used for delivering video content to accessory 220.)

Alternatively, PMD 202 can use the RemoteGUIImageData command described above. At block 512, accessory 220 can display the remote GUI image. In some embodiments, accessory 220 displays the image as received and does not modify it; thus, PMD 202 can control the look and feel of the remote GUI. Blocks 510 and 512 can be repeated until user input is detected; for example, PMD 202 can repeatedly send the same remote GUI image at the refresh rate of the display device of accessory 220.

At block 514, accessory 220 detects user operation of one of input controls 222. At block 516, accessory 220 can forward the user input to PMD 202, e.g., using the ProcessUserInput command or the type-specific input commands (e.g., ButtonInput, RotationInput, TouchInput) described above. As noted above, the command can indicate which control was operated and, if applicable, the nature of the operation. Accessory 220 can forward the user input without processing it to identify a responsive action to be taken; instead, accessory 220 can simply forward an identification of the detected user action.

At block 518, PMD 202 can process the user input to determine an operation (or action) to be performed in response. At block 520, if the operation does not correspond to exiting the remote GUI mode, process 500 proceeds to block 522, where PMD 202 performs the operation requested by the user. Any operation made accessible through the remote GUI image can be performed, such as starting playback, pausing playback, adjusting settings, browsing or searching a database, and so on. Performing some operations may involve sending commands from PMD 202 to accessory 220 (e.g., to change settings such as volume, display brightness, etc.). Performing other operations (e.g., playback) may involve sending media content from PMD 202 to accessory 220. Still other operations (e.g., database queries) can be performed by PMD 202 without sending commands or content to accessory 220. At block 524, PMD 202 can generate an updated remote GUI image based on the selected operation. Process 500 can then return to block 512 to display the updated remote GUI image. It should be noted that some operations, such as playback, can be ongoing, and a playing track (or sequence of tracks) can continue to play while process 500 iterates. (Playback can be stopped, e.g., by the user selecting a pause or stop operation, which selection can be processed using process 500.)

Process 500 can continue until such time as a user selects an operation that entails exiting remote GUI mode at block 520. At that point, process 500 ends (block 526). In some embodiments, PMD 202 can signal accessory 220 that the remote GUI mode is ending, e.g., using the ExitRemoteGUIMode command described above. Thereafter, accessory 220 can return to its local GUI operating mode.

In some embodiments, PMD 202 can remain connected to accessory 220 after exiting remote GUI mode. Thus, PMD 202 can continue to send media content to accessory 220, so that a playing track can continue to play even after remote GUI mode is exited. Thus, for example, if accessory 220 is incorporated into a console of an exercise machine, the user may exit the remote GUI to change workout settings while a song or video continues to play. As another example, if accessory 220 is incorporated into an automobile dashboard console that also provides navigation functionality, the user can exit remote GUI mode to perform navigation operations while music continues to play.

Further, in some embodiments, accessory 220 can support a user input that, when selected, instructs accessory 220 to re-enter remote GUI mode. Because PMD 202 remains connected, accessory 220 can send an EnterRemoteGUIMode command in response to detecting this user input. Thus, the user can enter and exit the remote GUI mode as desired, controlling PMD 202 through the remote GUI mode and controlling other features of accessory 220 through a local user interface.

In other embodiments, accessory 220 can provide source-selection input controls that allow a user to select among multiple sources of audio and/or video signals. For example, accessory 220 can be implemented in an in-vehicle head unit that also supports AM, FM, and/or satellite radio receivers; a GPS-based navigation system; environmental controls (e.g., adjusting a cabin thermostat); and so on, in addition to the remote GUI functionality provided by PMD 202. The head unit may provide buttons (or other user input controls) associated with selecting among these functionalities. The head unit may, but need not, map such buttons to the remote GUI. For instance, if the user operates a button to request an alternate audio source (e.g., FM radio) during remote GUI operation, the head unit can interpret the request and switch the audio source. In some embodiments, the head unit can notify PMD 202 of the change, e.g., using a SetStatusInfo command as described above. When the audio and/or video source is switched away from PMD 202, PMD 202 can continue to generate the remote GUI image or not, depending on implementation. In one embodiment, PMD 202 continues to generate the remote GUI image regardless of audio source selection but discontinues generating the remote GUI image if the video source selection is switched away from PMD 202.

It will be appreciated that process 500 is illustrative and that variations and modifications are possible. Steps or blocks described as sequential may be executed in parallel, order of steps may be varied, and steps may be modified or combined. Commands and communication protocols other than those described herein can be implemented to allow a portable media device to provide a remote GUI image to an accessory and to process user input responsive to the remote GUI image.

FIG. 6 is a flow diagram of a process 600 for operating an accessory (e.g., accessory 220 of FIG. 2) in conjunction with a PMD (e.g., PMD 202 of FIG. 2) that provides a remote GUI according to an embodiment of the present invention. Process 600 starts (block 602) when accessory 220 becomes connected to PMD 202. At block 604, accessory 220 can send identification and authentication information to PMD 202. In some embodiments, the identification information can include an indication that accessory 220 is capable of using the remote GUI functionality of PMD 202 and can also include configuration information for the accessory's display and/or input controls. For example, the AccessorySettings command and/or SetDisplayInfo and SetControlInfo commands described above can be used. Authentication, where provided, may include exchanging digital certificates and/or cryptographic messages with PMD 202. In some embodiments, authentication can be unidirectional (e.g., accessory 202 authenticates itself to PMD 202 or vice versa) or bidirectional (e.g., each device authenticates itself to the other). During identification and authentication, accessory 220 and PMD 202 can also exchange messages regarding which version of a remote GUI protocol and/or supporting software program each implements.

If identification or authentication fails at block 604, process 600 can exit (not explicitly shown). For example, PMD 202 can decline further communication with accessory 220 if accessory 220 fails to authenticate itself As another example, if the version of a remote GUI generation program used by PMD 202 is not compatible with or not approved by accessory 220, accessory 220 can determine not to enter remote GUI mode.

If, however, identification and authentication at block 604 succeed, process 600 proceeds to block 606. At block 606, accessory 220 can obtain options related to the remote GUI from PMD 220, e.g., using the GetPMDOptions and RetPMDOptions commands. For example, accessory 220 can send the GetPMDOptions command to determine which functionalities PMD 202 is capable of exposing via the remote GUI. At block 608, accessory 220 can select one or more functionalities that should be exposed, e.g., using the SetPMDOptions command.

At block 610, accessory 220 can instruct PMD 202 to enter remote GUI mode, e.g., using the EnterRemoteGUIMode or SetUIMode command described above. In some embodiments, accessory 220 automatically instructs PMD 202 to enter remote GUI mode after establishing that a particular PMD is compatible with the accessory's level of support for remote GUI mode. In other embodiments, accessory 220 can wait for user input or another event indicating that remote GUI mode should be entered before instructing PMD 202 to enter remote GUI mode.

At block 612, accessory 220 receives and displays a video signal from PMD 202; in general, this video signal can provide a remote GUI screen image and/or other image(s). For example, if PMD 202 is being operated to play back video content, the signal can include the video content. If PMD 202 is being operated to display stored still images (e.g., photos), the signal can include a still image.

In some embodiments, the video signal is an analog signal intended to cover the entire screen, and accessory 220 can simply generate display pixels in response to the video signal. In other embodiments, the remote GUI image covers only a portion of the screen, and accessory 220 can blend the video signal from PMD 202 with a signal from another source that provides the image for the rest of the screen. Digital video signals in various formats can also be used.

At block 614, accessory 220 determines whether user input is being received. If so, accessory 220 processes the user input. More specifically, at block 616, accessory 220 determines whether the input is “local” input. For example, as described above, accessory 220 may reserve some of the input controls as not being mapped to remote GUI functions, such as controls allowing the user to switch audio or video sources, or the like. Such reserved controls provide “local” input that accessory 220 can process rather than forwarding to PMD 202. If such local input is received, then the local input is processed by accessory 220 at block 618.

At block 620, accessory 220 determines whether the remote GUI mode should be exited in response to the local input. If so, at block 622, accessory 220 instructs PMD 202 to exit remote GUI mode, e.g., using the SetUIMode or ExitRemoteGUIMode commands described above, and process 600 ends (block 624). Otherwise, process 600 returns to block 612 and accessory 220 continues to receive and display a video signal from PMD 202.

If, at block 616, user input other than local input is detected, accessory 220 reports the user input to PMD 202 at block 626. Depending on implementation, the ProcessUserInput command or a type-specific input command (e.g., ButtonInput, RotationInput, TouchInput commands) described above can be used to report user input to PMD 202. These commands can indicate that a particular input event occurred while allowing PMD 202 complete control over how the event is interpreted and whether it has any effect on the displayed remote GUI image.

As described above, in some embodiments, accessory 220 continues to send commands reporting user input to PMD 202 for as long as the user continues to operate a control and sends a final command to indicate that the operation has ended. The reported user input may or may not affect the appearance of the remote GUI; any changes can be made by PMD 202 without any intervention by accessory 220 (other than reporting the user input). In addition the reported user input may result in PMD 202 invoking its own functionality, e.g., playing a track, initiating a phone call, or the like; again, accessory 220 does not need to interpret the user input or determine what functionality to invoke.

Regardless of whether user input is detected at block 614, process 600 can also check at block 628 to determine if any state changes have occurred in the operating environment of accessory 220. For example, in a vehicle, if the headlights are turned on or off, the changed state of the headlights can be a detectable change in the operating environment. In a console of an exercise machine, the beginning or ending of a workout can be a detectable change. As yet another example, as described above, accessory 220 can detect when the user changes the selected input source for audio and/or video. At block 630, accessory 220 can report a detected state change to PMD 202, e.g., using the SetStatusInfo command described above. As with user input, status changes may result in PMD 202 modifying the remote GUI image and/or invoking its own functionality. Accessory 220 does not need to determine or specify what (if any) effect a particular state change should have; it can simply report various state changes to PMD 202.

In some embodiments, accessory 220 can also respond to a detected state change by determining that the selection of PMD functionality to be exposed via the remote GUI should be changed. For example, if accessory 220 is an in-vehicle head unit, accessory 220 may be able to determine when the vehicle transitions into or out of a “parked” state (e.g., by detecting when an automatic transmission is shifted into or out of Park or by detecting when a parking brake is engaged or disengaged). In some embodiments, accessory 220 can allow certain functionality that is unavailable when the vehicle is not parked (e.g., video playback or third-party application programs that may cause unacceptable driver distraction) to become available when the vehicle is parked. Accordingly, notifying PMD 202 of a state change at block 630 can include sending a new SetPMDOptions command to change the selection of functionalities to be exposed via the remote GUI in addition to or instead of providing another state-change notification.

Process 600 can continue indefinitely while accessory 220 continues to receive and display video signals from PMD 202 and to report user input and state changes to PMD 202. Process 600 can end, e.g., when accessory 220 determines at block 620 that remote GUI mode should be exited. Once process 600 ends, it can be restarted, e.g., when accessory 220 reconnects to PMD 202. In some embodiments, accessory 220 can provide a user input control that can be operated to re-enter the remote GUI mode without requiring disconnection and reconnection; such an accessory can re-enter process 600, e.g., at step 610, as long as the accessory remains connected to the PMD.

It will be appreciated that process 600 is illustrative and that variations and modifications are possible. Operations described as sequential may be executed in parallel, order of operations may be varied, and operations may be modified, combined, added or omitted. For instance, those skilled in the art will appreciate that while a cycle of operations to check for user input and state changes may be suggested by the flow diagram, other implementations (e.g., based on interrupts) are possible. In some embodiments, PMD 202 can determine under certain conditions that remote GUI mode should be exited and exit remote GUI mode without receiving an exit command from accessory 220. Depending on implementation, PMD 202 might or might not notify accessory 220 when PMD 202 decides to exit remote GUI mode.

FIG. 7 is a flow diagram of a process 700 for remote GUI operation that can be executed in a PMD (e.g., PMD 202 of FIG. 2) according to an embodiment of the present invention. Process 700 starts (block 702) when an accessory (e.g., accessory 220 of FIG. 2) becomes connected to PMD 202. At block 704, PMD 202 can receive identification and authentication information from accessory 220. In some embodiments, the identification information can include an indication that accessory 220 is capable of using the remote GUI functionality of PMD 202 and can also include configuration information about the accessory's display and/or input controls. For example, the AccessorySettings command and/or SetDisplayInfo and SetControlInfo commands described above can be used. Authentication, where provided, may include exchanging digital certificates and/or cryptographic messages between PMD 202 and accessory 220. In some embodiments, authentication can be unidirectional (e.g., accessory 202 authenticates itself to PMD 202 or vice versa) or bidirectional (e.g., each device authenticates itself to the other). During identification and authentication, PMD 202 and accessory 220 can also exchange messages regarding which version of a remote GUI protocol and/or supporting software program each implements.

If identification or authentication fails at block 704, process 700 can exit (not explicitly shown). For example, PMD 202 can decline further communication with accessory 220 if accessory 220 fails to authenticate itself

After successful identification and authentication, process 700 can proceed to block 706. At block 706, PMD 202 can provide information related to remote GUI options to accessory 220. In some embodiments, the information can be provided in response to a request from accessory 220; for instance, PMD 202 can receive the GetPMDOptions command described above and provide the options using the RetPMDOptions command described above. At block 708, PMD 202 can receive instructions from the accessory regarding functionalities to be exposed in the remote GUI; for example, PMD 202 can receive a SetPMDOptions command from accessory 220. In some embodiments, at block 708, PMD 202 can also receive a SetDisplayRules command (or other information specifying display rules) from accessory 220.

At block 710, PMD 202 can enter remote GUI mode. In some embodiments, PMD 202 enters remote GUI mode only on instructions from accessory 220. For example, PMD 202 can receive the EnterRemoteGUIMode or SetUIMode command described above. In some embodiments, if the version of a remote GUI generation program used by PMD 202 is not compatible with or not approved by accessory 220, accessory 220 can determine not to enter remote GUI mode, in which case process 700 would not proceed past block 710.

At block 712, PMD 202 generates a remote GUI image and transmits a corresponding video signal to the accessory. In some embodiments, the video signal can be transmitted using analog or digital video output pins of PMD 202; in other embodiments, the RemoteGUIImageData command described above can be used.

Generation of the remote GUI image can be similar to that described above with reference to FIG. 5. In some embodiments, the remote GUI image for any particular operating condition is based on the PMD's native GUI image. The native GUI image can be modified to take into account characteristics of the accessory's display, such as size (in pixels or physical dimensions), aspect ratio, color depth, and the like. An image element supplied by the accessory can also be incorporated into the remote GUI image. In some embodiments, the image can be modified to reflect the location of accessory input controls; however, as described above, this is not required. The remote GUI image can also be adapted to the operating environment of a particular accessory (e.g., making GUI elements larger and/or easier to read if the accessory is in an automobile or other vehicle), to display rules specified by the accessory (e.g., using the SetDisplayRules command), and/or to the operating status of the accessory (e.g., day or night mode). The selection of which functionality to expose can be based on environment and/or status information, or the selection can be based on explicit instructions from the accessory (e.g., a SetPMDOptions command).

At block 714, PMD 202 determines whether a command has been received from accessory 220. If not, PMD 202 can continue to generate remote GUI images (or simply resend the same remote GUI image) at block 712 until a command is received. If a command is received at block 714, PMD 202 processes the command.

More specifically, at block 716, PMD 202 determines whether the received command indicates that remote GUI mode should be exited (e.g., the ExitRemoteGUIMode or SetUIMode commands described above). If so, PMD 202 stops generating remote GUI images at block 718, and process 700 ends (block 720).

If, at block 716, the received command does not indicate that remote GUI mode should be exited, then at block 722, PMD 202 determines whether the command indicates user input received by accessory 220. For example, PMD 202 can receive the ProcessUserInput command or any of the type-specific input commands (e.g., ButtonInput, RotationInput, TouchInput commands) described above, or other commands indicative of user input. If user input is received, then at block 724 PMD 202 processes the user input.

Processing the user input at block 724 can include a number of different operations depending on the specific input received and the current state of the remote GUI. For example, if the remote GUI is currently displaying a list of items, one of which can be highlighted, certain user input (e.g., operation of up or down buttons, turning of a wheel or knob, a swipe gesture on a touch screen) can be interpreted as scrolling the list or moving the highlighting to a different item. PMD 202 can update the remote GUI image to show a different highlighted item or a different portion of the list (or both) based on the user input.

Similarly, if the remote GUI is currently displaying a list of items, certain user input (e.g., operation of a select button, releasing of a wheel or knob, a tap gesture on a touch screen) can be interpreted as selecting an item (e.g., the currently highlighted item). PMD 202 can determine which item is being selected and invoke a functionality associated with the selected item. For example, if the selected item is a media track, PMD 202 can initiate playback of the track; if the selected item is an icon associated with a PMD functionality (e.g., telephone), PMD 202 can invoke that functionality; if the selected item is an icon associated with a particular application, PMD 202 can launch the application; and so on. Thus, processing the user input at block 724 can include updating the remote GUI image to reflect the user input and/or invoking functionality of PMD 202 based on the user input. After processing the user input, PMD 202 can continue to transmit the remote GUI image (with any applicable updates) at block 712.

If, at block 722, the received command is not a user input command, then at block 726 PMD 202 can determine whether the received command is indicative of a state change in the accessory, e.g., the SetStatusInfo command described above. If so, then PMD 202 can process the state change at block 720. Depending on the particular state change indicated, processing of the state change might or might not include updating the remote GUI image. For example, if the state change indicates a transition from day to night mode, the remote GUI image can be updated to reflect a “night-mode” color scheme. If the state change indicates that the accessory is switching away from using PMD 202 as a video input source, PMD 202 can suspend updating and/or transmitting remote GUI images until a subsequent state change command indicates that the accessory is switching back to using PMD 202 as a video input source. Other state changes can affect the selection of functions to be exposed via the remote GUI (e.g., the PMD can receive a new SetPMDOptions command or can determine based on the state-change information that the selection should change), and the remote GUI image can be updated to reflect the currently available functions. Still other state changes can affect ongoing operations within the PMD. For example, in an embodiment where PMD 202 is used with an in-vehicle head unit as accessory 220, PMD 202 can automatically pause or exit video playback if accessory 220 signals that the vehicle has been taken out of a parked state. After processing the state change, PMD 202 can display the remote GUI image (with any applicable updates) at block 712.

If, at block 726, it is determined that the received command is not a state change command, then at block 730, the command is processed. In some embodiments, some commands are ignored during remote GUI mode operations; for example, commands requesting information about stored content on PMD 202 can be ignored. (The user can access such information via the remote GUI without PMD 202 needing to supply any information to the accessory.) Other commands, however, can be accepted and processed at block 730. For example, some accessories have buttons associated with playback control (e.g., play/pause, fast-forward, and rewind buttons), and commands invoking PMD functions associated with playback control can be processed at block 730, thereby allowing a user to use the accessory's buttons in an intuitive way.

Process 700 can continue indefinitely, with PMD 202 continuing to generate and transmit remote GUI images that it updates based on command input from accessory 220 and to invoke its internal functions based on user input relayed by accessory 220. Process 700 can end, e.g., when PMD 202 receives a command indicating that remote GUI mode should be exited or when accessory 220 becomes disconnected from PMD 202. Once process 700 ends, it can be restarted, e.g., when PMD 202 reconnects to accessory 220. In some embodiments, after exiting remote GUI mode, PMD 202 can accept a subsequent command from accessory 220 to re-enter remote GUI mode without requiring disconnection and reconnection; in such embodiments, PMD 202 can simply re-enter remote GUI mode at block 710.

It will be appreciated that process 700 is illustrative and that variations and modifications are possible. Operations described as sequential may be executed in parallel, order of operations may be varied, and operations may be modified, combined, added or omitted. For instance, those skilled in the art will appreciate that while a cycle of operations to check for user input and state changes may be suggested by the flow diagram, other implementations (e.g., based on interrupts) are possible. In some embodiments, PMD 202 can determine under certain conditions that remote GUI mode should be exited and exit remote GUI mode without receiving an exit command from accessory 220. Depending on implementation, PMD 202 might or might not notify accessory 220 when PMD 202 exits remote GUI mode.

As noted above, a PMD can expose any of its functionalities via the remote GUI. FIG. 8 illustrates a native GUI on a PMD 800 that has a number of different functionalities. Native GUI image 802 includes a number of icons displayed on a touchscreen 804 of PMD 800. The user can touch an icon to select the associated functionality. For example, icon 806 is associated with media player functionalities (including audio and video playback); icon 808 is associated with a web browser; icon 810 with telephony; icon 812 with maps and navigation aids; and so on.

FIG. 9A illustrates a remote GUI image associated with the native GUI of PMD 800 according to an embodiment of the present invention. Remote GUI image 900 is displayed on a display screen 902 of an accessory 904 that has associated control buttons 906 a-e (e.g., up, down, left, right, select). Remote GUI image 900 includes icons that look generally like the icons of native GUI image 802, and the user can activate functionalities of PMD 800 by selecting the corresponding icon using control buttons 906 a-e. In the embodiment shown, one of the icons is highlighted with cursor 908 to indicate that it will be activated if the user presses select (SEL) button 906 e. Thus, icon 910 (media player) is currently highlighted. A user can change the selection by operating arrow buttons 906 a-d to move cursor 908 up, left, right, or down and select an icon using the select (SEL) button 906 e.

In the embodiment shown, not all functionalities of PMD 800 are exposed via the remote GUI, and icons corresponding to functionalities not exposed are not drawn in remote GUI image 902. Thus, for example, web browsing (icon 808) is not available. Other embodiments may provide the icons for unexposed functionalities in grayed-out or otherwise de-emphasized form so that the user can readily determine which functionalities are available for selection.

FIG. 9B illustrates a second remote GUI image 950 according to an embodiment of the present invention. Image 950 provides a selection menu for media player functionalities. In some embodiments, PMD 800 can generate image 950 when a user selects media player icon 910 in image 900 of FIG. 9A. Image 950 provides media playback options. Similarly to image 900 described above, image 950 provides a cursor 952 that the user can move by pressing buttons 906 a-d; the item currently highlighted by the cursor can be selected by pressing select button 906 e. In the example shown, video playback is not available (e.g., because accessory 900 has instructed PMD 800 not to expose this functionality); this is indicated by graying out “Videos” menu item 954. Alternatively, menu item 954 (or any other item corresponding to unexposed functionality) can simply be omitted from image 950.

It will be appreciated that the remote GUI images and controls described herein are illustrative and that variations and modifications are possible. For example, in some embodiments, if the accessory provides configuration information indicating that it has a touchscreen display, the cursor can be omitted. In some illustrated examples, the remote GUI images closely resemble the native GUI images, but this is not required. For example, a grid of icons in a native GUI image can be presented in a remote GUI as a list, or a list of items in the native GUI image can be presented in a remote GUI image as a grid, and so on. In some embodiments, the PMD generates remote GUI images that are similar or identical across different accessories, thus providing a consistent user experience. The particular functionalities shown are intended as illustrative and not limiting.

In the processes described above, a PMD generates a remote GUI image that is displayed by the accessory. As noted, it can be desirable for the PMD to adapt the remote GUI image to the environment of a particular accessory, e.g., complying with safety standards for an automobile. FIG. 10 is a flow diagram of a process 1000 for generating a remote GUI image that can be implemented in a PMD according to an embodiment of the present invention. Process 1000 can be incorporated into any of the processes described above.

At block 1002, a PMD can establish a connection to an accessory. As described above, establishing a connection provides a communication channel, and the connection can be wired or wireless (or a combination thereof) as desired.

At block 1004, the PMD can receive configuration information from the accessory, including a display descriptor and a display rule. The configuration information can also include an instruction to enter remote GUI mode; in some embodiments, the PMD waits to enter remote GUI mode until the accessory instructs it to do so.

The display descriptor can include any information descriptive of a display of the accessory, such as height and width of the screen (or a portion thereof that has been allocated to remote GUI images) in absolute dimensions, resolution of the screen (or relevant portion thereof) in pixels, color depth, signal format, and the like.

Other information useful in assessing the appearance of an image, such as distance from the screen to the user, can also be provided in a display descriptor. In some embodiments, such as automobiles, the user can be a driver who sits in relatively fixed relation to an in-dash console. The distance from the screen to the user can be specified as a range (e.g., based on the range of seat positions provided by the automobile), a minimum distance (e.g., corresponding to seat in its forward-most position), or a maximum distance (e.g., corresponding to seat in its rearward-most position). In some embodiments, the automobile may be able to determine the current seat position for a given driver and provide a current distance based on the current seat position.

A display rule received at block 1004 can specify particular features or qualities that a displayed image should have. Examples of display rules include minimum character size (height and/or width) and minimum spacing or pitch between lines. FIG. 11 illustrates one implementation of defining character height for uppercase characters (distance indicator 1102) and lowercase characters (distance indicator 1104), and line pitch, i.e., distance between adjacent lines (distance indictor 1106). Also illustrated are examples for defining character width (distance indicator 1108) and horizontal pitch or kerning (distance indicator 1110). Any or all of these attributes can be defined by display rules. Minimum sizes can be specified in absolute units (e.g., inches or centimeters), and size can be defined based on on-screen measurements or apparent size (e.g., angular size) based on the user's position relative to the screen.

Other display rules related to formatting of on-screen text can also be specified, e.g., requiring a certain amount of space between lines of text, maximum number of lines per screen, maximum number of characters per line, particular fonts to be used, or the like.

In addition to or instead of character-size rules, other display rules can also be provided. Examples include rules specifying a minimum size of graphical objects such as icons (e.g., the icons shown in FIG. 9A) or on-screen control elements (e.g., arrows 153 and 155 in FIG. 1C), and rules specifying color schemes or minimum contrast requirements. Display rules can be presented using any suitable data structure or format (e.g., key-value pairs).

In some embodiments, a set of display rules can be defined and stored in the PMD in association with a rule identifier. For example, in the case of automobiles, different nations or regions can have different safety standards that restrict the amount or density of information that can be presented on a console screen, the fonts or size of text that can be used, or the like. Such rules can be stored in association with a region code identifying the nation or region in which these rules apply. At block 1004, the PMD can receive a region code and retrieve the associated display rules from its internal storage.

Based in part on the display descriptor and display rules, the PMD can generate a remote GUI image (block 1006). Block 1006 can be executed after the PMD is instructed by the accessory to enter remote GUI mode, or portions of block 1006 can be executed in preparation for such an instruction.

In some embodiments, the remote GUI image presents information similar to that which can be presented on the PMD's own display (e.g., as shown in FIGS. 1A-1C and FIGS. 8 and 9A-9B), with adaptations based on the display descriptor and display rules. For example, display rules can be used in determining the amount of text and/or number of icons to be displayed on the screen. Referring again to FIG. 10, in some embodiments, at block 1008, the PMD can calculate a character size in pixels based on the display descriptor and display rules. In one such embodiment, the display descriptor can include the display height in centimeters and vertical resolution in pixels, and the display rule can specify a minimum character height in centimeters, as measured at the screen. To compute a character height in pixels, the PMD can divide the display height by the vertical resolution to determine a pixel height (in centimeters in this embodiment). The PMD can then divide the minimum character height specified in the design rule by the calculated pixel height to determine a character height in pixels. Similar calculations can be done for horizontal character size in pixels. (In some embodiments, the horizontal size is determined by the vertical size and a font selected by the PMD or specified by the display rules.)

At block 1010, the PMD can calculate a line pitch in pixels, based on the display descriptor and a display rule that specifies the minimum line pitch in centimeters, as measured at the screen. The minimum character pitch in pixels can be computed by dividing the minimum character pitch in centimeters by the pixel height. (Kerning, or horizontal character pitch, can be determined similarly.)

FIG. 11 illustrates character size parameters that can be specified by display rules according to an embodiment of the present invention. Menu 1100 consists of a number of selectable items that include image and text elements. As illustrated, display rules can specify any or all of an uppercase character height 1102, lowercase character height 1104, line pitch 1106, character width 1108, and character spacing (or kerning) 1110. In some embodiments, the size and pitch parameters specified by the design rule can be treated as minimum values, and the PMD can use larger values (thus producing larger text or larger spacing) but not smaller values. It is to be understood that it is not necessary to specify all of the parameters illustrated in FIG. 11. For example, it may suffice to specify uppercase character height 1102 and line pitch 1106, allowing other parameters to be determined based on the font used. The font itself can be selected by the PMD or specified in a display rule.

In some embodiments, the display rule can specify a minimum apparent character size and/or line pitch as measured at the user's viewing location. For instance, as shown in FIG. 12, the display rule can specify a minimum angular size δ. The actual size depends on the distance D from the viewer (point 1202) to the display device. Thus, for a display device 1204 at distance D₁, the actual size required to produce angular size δ is h₁; for a display device 1206 at a larger distance D₂, the actual size would be h₂, which is larger than h₁. The actual size h to produce a desired angular size δ at distance D can be determined using the formula h=2*D*tan (δ/2). Once the actual size h is known, the PMD can use the techniques described above to determine the size in pixels that will produce an image with actual size h.

Referring again to FIG. 10, at block 1012, using the character size and pitch information in combination with the known display size or resolution, the PMD can determine limits on the number of characters per line and/or number of lines per screen. For example, using a line pitch in pixels (determined at block 1010) and a vertical display resolution in pixels (specified in the display descriptor), the PMD can compute the maximum number of lines per screen. Similarly, using character pitch in pixels and a horizontal display resolution in pixels provided in the display descriptor, the PMD can compute the maximum number of characters per line. In other embodiments, limits on lines per screen and/or characters per line can be directly specified in a display rule.

At block 1014, the PMD can determine a scrolling speed based in part on the maximum number of lines per screen. The scrolling speed can determine, e.g., how fast to update the remote GUI image when a user operates a scrolling control such as arrows 153 or 155 in FIG. 1C. For example, slower scrolling speeds may be desirable where fewer lines appear on the screen. Other parameters related to updating can also be determined.

At block 1016, the PMD can select information and control elements to be displayed in the remote GUI image. The selection of information elements can depend in part on the current state of the PMD, which can depend on prior user input. Thus, for example, in one state, the remote GUI image can display a list of album titles; if the user selects an album, the remote GUI image can be updated to display a list of track titles for tracks from the selected album.

The selection of information elements can also depend in part on the amount of available space. One aspect of selecting information elements can include determining how many media assets or other options to represent on a single screen, and this can be determined, e.g., based on the maximum number of lines per screen. Another aspect relates to selecting information about each media asset or other option. For instance, the local GUI of some PMDs can display a list of tracks with the album name and or artist name under each track in smaller print. Where the amount of information that can be displayed is more limited, the remote GUI image can include less information; for example, just the track title might be included, or the track title followed by the artist name on the same line might be included.

Control elements can be selected based in part on the user input controls, to the extent that information about user input controls is provided to the PMD. Thus, for example, if a touchscreen control is available, touchable control elements for navigating a menu or playing a track (e.g., as shown in FIG. 1C) can be included. The size of such elements can be determined based on properties of the touchscreen as specified by the accessory (e.g., using the AccessorySettings command described above).

At block 1018, the PMD can arrange the information and control elements into a screen image. In some embodiments, this can include populating an image buffer or other data-storage array with pixel values representing the image as a color for each pixel. Where text is being displayed, pixel colors can be determined based on characters to be displayed and pre-stored patterns associated with a particular font that can be scaled to the desired size. For a graphical element such as an icon, a pre-stored icon can be scaled to the desired size. Pixel color can be further influenced by environment information (e.g., in the case of a vehicle, whether to operate in day or night mode).

At block 1020, the PMD can generate a video signal based on the screen image. A particular signal format or technique for converting pixel color data to a video signal is not required, and any signal format that is recognizable to the accessory can be used.

It will be appreciated that process 1000 is illustrative and that variations and modifications are possible. Steps described as sequential may be executed in parallel, order of steps may be varied, and steps may be modified, combined, added or omitted. For example, while the process is described with reference to characters and text information, graphical elements such as icons and/or images can also be included in a remote GUI image. Accessory-provided display rules can be used in determining the size, number, and arrangement of graphical elements. In addition, the PMD can select information or control elements to include based on accessory-provided information indicating supported functionalities (e.g., as described above).

To update a remote GUI image, the PMD can repeat portions of process 1000, e.g., selection and arrangement of information elements (and control elements if desired) at blocks 1016 and 1018. The PMD generally does not need to recompute characters per line, lines per screen or other parameters that can affect information selection, unless the accessory sends a new display descriptor or display rule. In some embodiments, the accessory is not permitted to change its display descriptors or display rules during remote GUI operation; for example, the PMD can require that display descriptors and display rules be sent prior to entering remote GUI mode and can ignore any further display descriptors or display rules that are sent while the PMD is operating in remote GUI mode.

The use of accessory-supplied display rules can allow the accessory (or its manufacturer) to retain at least some control over the appearance of the remote GUI image, even though the image itself is generated by the PMD. Thus, an accessory manufacturer can assure compliance with applicable safety rules and/or provide a more user-friendly interface (e.g., by avoiding small type that may be difficult for a user to read).

In some embodiments, the accessory can verify the identity of the PMD and/or the version of the remote GUI software that is in use by the PMD prior to instructing the PMD to enter remote GUI mode. For example, the accessory can store a valid digital certificate associated with a public key. Prior to entering remote GUI mode, the accessory can require the

PMD to present a matching certificate and/or encode a random challenge using a private key associated with the public key in the certificate.

In some embodiments, the accessory can also store a list of allowable versions of the remote GUI software. Prior to entering remote GUI mode, the accessory can determine the version of the remote GUI software supported by the PMD and verify that the supported version corresponds to an allowable version. (In some embodiments, a PMD can support multiple versions of the remote GUI software, and the accessory can select an allowable version from among the supported versions.)

While the invention has been described with respect to specific embodiments, one skilled in the art will recognize that numerous modifications are possible. For example, although embodiments described above may make specific reference to playback of media content, a portable media device may also provide other functionality such as personal information management, mobile telephony, and so on. In other embodiments, any of this functionality can be made accessible through a remote GUI. Thus, for example, another remote GUI implementation may provide a hands-free telephone interface, e.g., for the driver of an automobile. The driver can operate the remote GUI to answer or place telephone calls, and the call can be conducted using a speaker and microphone controlled by the accessory, together with the mobile phone connection of the PMD. The remote GUI for telephony can resemble the PMD's native GUI for telephony, thus providing the user with a more intuitive interface and potentially reducing distraction related to operating an unfamiliar remote interface.

In addition, embodiments described above may make reference to a portable media device supplying the entire image that is displayed on the accessory. In one alternative embodiment, the remote GUI image supplied by the portable media device can be displayed in a portion of the accessory's display screen while image data from other sources is displayed in other portions of the screen. For example, an accessory may designate a rectangular area within the display device for the remote GUI. The portable media device can deliver pixel data (e.g., in digital or analog form) for the remote GUI area of the display while the accessory determines the pixels for the rest of the display. For example, the accessory can use a portion of the display for displaying navigation information while another portion is used for the remote GUI. For portions of the display not in the remote GUI area, the portable media device can provide placeholder data (e.g., black pixels in an analog video stream) or no data. (If the accessory has a touchscreen as a user input control, the accessory can selectively forward user input signals indicating a touched portion of the screen to the media player based on whether the touched portion is inside or outside the remote GUI area.)

While the embodiments described above may make reference to specific hardware and software components, those skilled in the art will appreciate that different combinations of hardware and/or software components may also be used and that particular operations described as being implemented in hardware might also be implemented in software or vice versa.

Computer programs incorporating various features of the present invention may be encoded on various computer readable media for storage and/or transmission; suitable media include magnetic disk or tape, optical storage media such as compact disk (CD) or DVD (digital versatile disk), flash memory, and the like. Computer readable media encoded with the program code may be packaged with a compatible device or provided separately from other devices (e.g., via Internet download).

Thus, although the invention has been described with respect to specific embodiments, it will be appreciated that the invention is intended to cover all modifications and equivalents within the scope of the following claims. 

1. A method for operating a portable media device, the method comprising, by the portable media device: establishing a connection to an accessory having a display device and a user input control; receiving configuration information from the accessory, the configuration including a display descriptor and a display rule; determining, based at least in part on the display descriptor and the display rule, information content for a remote graphical user interface image; generating the remote graphical user interface image including the information content; sending a video signal to the accessory, the video signal representing the remote graphical user interface image; while sending the video signal, receiving a command from the accessory, the command reporting an operation of the user input control of the accessory; and modifying the remote graphical user interface image based on the reported operation of the user input control, wherein the modified remote graphical user interface image is subsequently represented in the video signal.
 3. The method of claim 1 wherein the display rule includes a specification of a minimum character size.
 4. The method of claim 1 wherein the display rule includes a region code, the method further comprising: determining a minimum character size based on the region code.
 5. The method of claim 3 wherein the minimum character size is specified as an angular size and wherein the display descriptor includes a screen distance parameter, the method further comprising: determining a minimum character size in pixels based on the angular size and the screen distance parameter.
 6. The method of claim 3 further comprising: determining a maximum number of lines of text for an image based at least in part on the minimum character size.
 7. The method of claim 3 further comprising: determining a maximum number of characters per line of text for an image based at least in part on the minimum character size.
 8. A computer program product comprising a computer-readable storage medium encoded with program instructions that, when executed by a processor in a portable media device, cause the portable media device to execute a method, the method comprising: establishing a connection to an accessory having a display device and a user input control; receiving configuration information from the accessory, the configuration including a display descriptor and a display rule; determining, based at least in part on the display descriptor and the display rule, an amount of information to be included in a remote graphical user interface image; selecting information content for the remote graphical user interface in compliance with the amount of information to be concluded; generating the remote graphical user interface image including the information content; and sending a video signal to the accessory, the video signal representing the remote graphical user interface image.
 9. The computer program product of claim 8 wherein the method further comprises: while sending the video signal, receiving a command from the accessory, the command reporting an operation of the user input control of the accessory; and modifying the remote graphical user interface image based on the reported operation of the user input control, wherein the modified remote graphical user interface image is subsequently represented in the video signal.
 10. The computer program product of claim 8 wherein the method further comprises: receiving from the accessory information descriptive of the user input control, wherein the information content for the remote graphical user interface image is determined based in part on the information descriptive of the user input control.
 11. The computer program product of claim 8 wherein the display descriptor includes a display size specified in a length unit and a display resolution specified in pixels, wherein the display rule includes a minimum character size, and wherein the method further comprises: determining a maximum number of lines of text for the remote graphical user interface image; selecting a plurality of items about which information is to be displayed in the remote graphical interface image; and selecting specific information to be displayed for each of the plurality of items based at least in part on the maximum number of lines of text.
 12. The computer program of claim 11 wherein the information items include a portion of a scrollable list of items and wherein the method further comprises: determining a scrolling speed for the scrollable list based at least in part on the maximum number of lines of text.
 13. A portable media device comprising: an accessory interface configured to communicate with an accessory; and a processor coupled to the accessory interface and configured to provide a plurality of functionalities invokable by a user, the processor being further configured to: receive configuration information via the accessory interface, the configuration information including display dimensions and a display rule; receive input commands via the accessory interface, the input commands indicating operation of a user input control of the accessory; generate remote graphical user interface images based at least in part on the received input commands, the display dimensions, and the display rule; and send a video signal via the accessory interface, at least a portion of the video signal corresponding to a most recently generated remote graphical user interface image.
 14. The portable media device of claim 13 further comprising a display device and wherein the processor is further configured to generate native graphical user interface images for the display device.
 15. The portable media device of claim 14 wherein the processor is configured to switch between generating the native graphical user interface images and generating the remote graphical user interface images in response to a mode selection command received via the accessory interface.
 16. The portable media device of claim 13 wherein the display dimensions include a display size specified in a length unit and a display resolution specified in pixels, wherein the display rule includes a minimum character size, and wherein the processor is further configured to: determine a maximum number of lines of text for the remote graphical user interface image; select a plurality of items about which information is to be displayed in the remote graphical interface image; and select specific information to be displayed for each of the plurality of items based at least in part on the maximum number of lines of text.
 17. A method for controlling a portable media device using an accessory, the method comprising, by the accessory: providing configuration information to a portable media device, the configuration information including display dimensions and a display rule specifying a minimum size of an image element; receiving from the portable media device a first image signal, wherein at least a portion of the first image signal communicates a first graphical user interface image, the first graphical user interface image being based at least in part on the display dimensions and the display rule; displaying an image including the first graphical user interface image on a display device of the accessory based on the first image signal; detecting user operation of an input control of the accessory; sending to the portable media device an input signal indicating that the input control was operated; receiving from the portable media device a second image signal, wherein at least a portion of the second image signal specifies a second graphical user interface image, the second graphical user interface image reflecting the operation of the input control; and displaying an image including the second graphical user interface image on the display device of the accessory.
 18. The method of claim 17 wherein the display dimensions include a display size specified in a length unit and a display resolution specified in pixels.
 19. The method of claim 17 wherein the display rule includes at least one of minimum character height or a minimum character width.
 20. The method of claim 17 wherein the display rule includes a minimum angular size of an image element.
 21. The method of claim 17 wherein the display rule includes a minimum size of an icon.
 22. An accessory comprising: a display device; a user input control; an interface configured to communicate with a portable media device; and a controller coupled to the display device, the user input control, and the interface, the controller being configured to: send configuration information to the portable media device via the interface, the configuration information including display dimensions and a display rule that specifies a minimum size parameter for a character; receive a video signal from the portable media device via the interface, the video signal encoding a graphical user interface image, wherein the graphical user interface image is in compliance with the display rule; control the display device to display an image based on the received video signal, the displayed image including the graphical user interface image; detect operation of the user input control; and send a signal to the portable media device via the interface to indicate the operation of the user input control.
 23. The accessory of claim 22 wherein the display rule includes a minimum character height expressed in units of length.
 24. The accessory of claim 22 wherein the display rule includes a minimum angular size.
 25. The accessory of claim 22 wherein the display rule includes a region code and wherein a minimum character height parameter is associated with the region code. 